A variety of cutters or bits are presently used in mechanical excavation systems. One type of cutter commonly used on cutterheads in rock excavation is a disc-type rolling cutter. For example, hardened steel disc cutters are frequently used on cutterheads employed in tunnel boring, raise drilling, large diameter blind drilling, and/or small diameter drilling systems.
In hard rock, the disc cutter may be used to apply great thrust on the cutter, and consequently pressure on the rock to be cut, a zone of rock directly beneath (i.e., in the cutting direction) and adjacent to the disc cutter is crushed, normally forming very fine particles. The crushed zone may form a hydraulic-like pressure downward (again, in the cutting direction) and outward against adjacent rock. The adjacent rock then cracks, and chips spall from the rock face being excavated. The crushed rock is then collected and removed as debris.
The service life of disc cutters can be a significant limitation in the operating efficiency of mechanical excavation systems using such cutters. For example, because the disc cutters are typically pushed against hard rock surfaces (i.e., tunnel faces) with very significant forces including high shock loads and work in an abrasive, high wear environment, the disc cutters can wear at a rapid rate. These disc cutters may be replaced. However, to change disc cutters, mechanical excavation systems can be stopped for several hours while the disc cutters are removed, replaced, and/or repaired. This time and effort intensive repair activity reduces the overall efficiency or rate of mechanical excavation systems using the disc cutters.
In addition, disc cutters typically include bearing systems that allow the disc cutters to rotate on the target surface as the cutterhead rotates. If this bearing system fails, the disc cutter can stop turning. When the disc cutter stops turning, the portion of the disc cutter in contact with the target surface slides. This sliding contact can wear the disc cutter rapidly into a flat, wide spot that no longer is able to apply adequate compressive force against the target surface to crush hard rock or other hardened material.
Therefore, manufacturers and users of disc cutters continue to seek improved disc cutter designs and manufacturing techniques.